Tanning of proteins



PatentedJan 28, 1941 7 TANNING orrnornms Paul B. Davidson, Wilkinsburg, Pa., assignor to Strathmore Paper Company, Springfield, Mass.,

a corporation of Massachusett Application December 4, 1940, Serial No. 368,538

1 No Drawing.

8 Claims. (01. lit- 1 54) This invention relates to the art of tanning water-dispensable proteins such as animal glues as applied to paper and like materials.

It is common practice in the manufacture of certain t pes of paper toapply asurface treatment or sizing of animal glue or starch to the p per for the purpose of imparting to the pa er certain characteristics such as strength, greater 10 resistance to the penetration of liquids such as inks. erasure properties. increased durability and permanence, and stiffness. In some specialty papers, such as blue print pa er, there are the added requirements of suihcient tensile strength and resistance to abrasion when the paper is wetted or soaked in water. This soaking in water is a necessary part of the developing of the exposed prints and is carried on with the paper under tension and the water is often applied under pressure.

A common prior way of sizing such paper is to pass the paper into a bath of animal glue and then between rolls that squeeze oil. the excess of glue. In the prior art; the glue is a p ied to the paper at a temperature of about 140 I. so that, due to its lower viscosity at this temperature. it will penetrate into the aper and produce a more or less complete saturation of the pa er with the glue, size, Aluminum sulphate (panermaker's alum) and formaldehyde have been added to the glue bath as tanning agents. for-developing hieh wet tensile st ength and resistance to abra ion when wet. This procedure has its undesirable features. such as the development of abnormally high viscosity of the glue, so that difilculty i encountered in the surfaceor tub-sizing opera- I tion. To eliminate this dimculty. employmenthas been made of a process 01'. omitting a tanning a ent from the glue bath and then giving the 40 freshly sized pa er. b fore it has been dried, a se a ate treatment with a tanning agent. Formaldehyde has been used in uch a treatment. There are various ways in w accom lished: thus. a water utl'on of the formaldehyde may be sprayed nto the freshly sized and undried paper or the paper may be passed through a bath containing the water solution of this tannin'g agent and the excess squeezed oil 50. before the paper is dried: or the paper may be passed through a chamber filled with, vaporized formaldehyde.

For some special types of paper, such as blue print paper, this method of glue sizing does not 55 in paper manufacture.

clythls mav be produce the best results, particularly with respect to wet strength.

Further, there are serious disadvantages to the use of formaldehyde as a. tanning agent, irrespective of the method by which it is applied. In

the drying of the paper and, for this reason, an

excess of the tanning agent must be originally applied so that satisfactory wet strength may be developed in the paper; and small variations in the drying of the paper cause varying quantities of the formaldehyde to be driven oii. with a corresponding change in the tanning efiiciency and in the strength characteristics of the product. Secondly, the accumulation of formaldehyde gas around open drying equipment for the paper may be so great that it produces irritating eil'ects and disagreeable working conditions. Thirdly, paper that has beendried, apparently when it is used due to the fact that there still remains in the .paper an appreciable amount of formaldehyde: with such papers as blue print papers, where the paper is subjected to drying after the printing operation, the evolution of formaldehyde may then cause a disagreeable odor to develop.

An object of this invention, therefore, is to eliminate these undesirable conditions and other disadvantages by the use of a water-soluble, sat;

urated, aliphatic dialdehydes as the tanning agent Dlaldehydes are sometimes called dials. Glyoxal is the diaidehyde of ethylene glycol. It can be obtained in its monomeric form by heating the polymer with phosphorus pentoxide; but the polymerized glyoxal can be used as such and is the material referred to in the specific, examples set forth hereinafter.

In its solid form it is a colorless solid material containing about 25 percent of water of hydration, has no odor, does not volatilize like formaldehyde, and has a tanning efllciency at leastv equal to that of formaldehyde.

A great advantage in the useof a dialdehyde agent applied remains in the paper to react with he glue.

Another advantage in the use of glyoxal is that times as great.

aerasee it produces greater wet strength in the paper than can be obtained with formaldehyde under the same conditions. with respect to theresistance to abrasion when the paper is wet with water. Under some con- This is particularly true dltions, glyoxal has been found to produce wet hyde and proteins, it would logically appear that glyoxal taming would depend, for its efficiency, upon the pH of the protein, which illustratively is animal glue- That is. formaldehyde reacts more rapidly and/ormore completely with glue of high pH value .(about 8.5) than with one of pH? and still more than with glue at a pH lower than the isoelectric point of the protein in the glue, as for example at a pH of 3.5. It has been found that this relationship between the pH of the glue and the tanning efficiency of glyoxal does not follow parallel to that of formaldehyde. Whereas formaldehyde produces decreasing strength with decreasing pH of the glue size, glyoxal produces wet strengths of the same magnitude substantially irrespective of the pH of the glue size. This is illustrated in the following table of results of experiments in which the same lot of paper was tub-sized with animal glue of varying pH and then passed through a bath of the taning agent, made up to a 2 percent concentration, the excess of solution was squeezed off by passing the papers between rolls, and the paper then dried at a temperature of 95: 5 degrees C.

Table I Wet tensile strength. with glue size of varying pH after a 24-hour aging period pH oi glue size .Tanning agent 2% formaldehyde 1070 1190 1280 131K) 1370 1110 1350 1370 2% glyoxal 1910 2000 2010 2110 2160 2160 2020 2040 Yet tensile values are expressed in grams per mm. width of test s p.

If, for any reason, the wet strengths are insufficient to meet certain demands, it has been Wet tensile strength with glue of varying pH after a 6 day doing period pH of glue size Tanning agent 2] formaldehyde 1110 1270 1320 1420 1400 1300 1340 1400 2%glyoxal 2120 2210 2100 2290 2410 2180 2210 2340 when a high pH glue solution is used, the uniformity of the desired properties also depends upon the proper buifering of the glue size at the required pH values. A presently preferred bufiering agent is borax, while magnesium oxide, magnesium carbonate and other combinations of materials as alkaline bufiering agents that will maintain the pH ofthe glue within the limits of about 8 to 9.5, may be employed. The quantity to be employed depends upon the engine sizing emciency; and this in turn depends upon the amount of papermakers alum, since the leaching of alum from the paper renders the employment of such a buffer necessary. A further factor in determining the quantity is the amount of paper to be sized with a given quantity of the size, as this likewise influences the possible amount of leaching.

In the mill scale preparation of the glue size, the following formulas are typical. In each case,

substantially 600 gallons ofglue sizing solution was prepared. EXAMPLE I High pH size (pH of 8.5)

.'(A) Animal glue (12.5% sol=110 M. P.

viscosity) lbs 300 Water gals 250 Sodium hydroxide grams 654 Preservative (sodium ortho-phenyl phenate) kg 28 J The sodium hydroxide was dissolved in the water, to which the glue was added and allowed to soak and swell for two hours, with brief agitation from time to time, and then steam-cooked at 130 degrees to 140 degrees F. to completely disperse the glue.

(Bl Water, gals 100 Bufler (borax) lbs 12 to 27 The hot glue dispersion (A) was then added, with stirring, to the solution B, and after thorough mixing was diluted to the desired Beaum, giving 600 gallons of glue sizing solu tion. Twelve pounds of a suitable filler may be suspended in solution B, if desired.

The effect of mixing brings the system to about the proper temperature for sizing, i. e., between degrees and 115 degrees 1.

EXAMPLE II Low pH size (pH of 4.2)

Glue lbs 300 Water gals 250 Hydrochloric acid (36 percent) liters 6.25

The hot glue solution was made up as in Example I, and then stirred into gallons of water, in which 12 lbs. of a suitable filler may be suspended. This cooled the glue below the temperature of any active hydrolysis; and the solution was then diluted to the desired Beaum, and gave substantially 600 gallons of glue sizing solution at the desired temperature.

The quantity of glue can be adjusted in accordance with its properties for obtaining the desired concentration and Beaum. The amount of alkali or acid added is sufficient to obtain the desired pH, between 3.5 and 9 or even higher being found effective: the specific pH value depends upon the ingredients and history of the paper being sized, and upon the desired viscosity .of the glue solution at the temperature of employment. In preparing glue sizes of high pH, the alkali may be sodium, potassium or ammonium hydroxide, or another proper alkaline material: successful glue sizes have been prepared with tertiary amines. When the pH value is high (above neutral) an alkaline buffering agent is introduced. When a low pH sizing solution is being prepared, the penetration of the alum of itself will lower the pH slightly and normally increase the viscosity of the glue; and this may be taken into account in determining the quantityoi acidifying agent to be utilized. In some cases, it has been found desirable to add inert fillers to the size to improve certain surface properties of the paper. That is to say,-it the "paper is to be treated with a water-dispersed system, such as dextrine adhesives, or a solution such as blue print coating solutions, the presence of a proper iiller often has desirable eflects. In the case of blue print paper, for example, it has been found days is substantially the same as that tanned with 2% formaldehyde solution.

when the paper is being-made for employment as a base for a blue print coating solution, it has that titanium dioxide and/or bentonite improves the color produced in the final prints. Some fillers (such as calcium sulphate) cannot be used for this specific purpose, for they are not inert and react unfavorably with sensitizing chemi cals. The paper is sized with such a solution by passing the paper through it, and then passing it through a solution containing about 2 percent of glyoxal and between 0.02 and 0.5 percent of a wetting agent, and is then dried.

Between the application of the sizing solution 1d of the wetting agent, the paper may be aged ii desired for the stabilization. A better product usually results when the paper is drawn through the solutions to produce a coating and treatment by adoiibleside dip.

The wetting agent is not invariably necessary, but is desirable for eliminating the last traces of white spots in blue prints. It has been discovered that not all wetting agents areof value in this process, but only those commonly known as neutral or cationic wetting agents serve the purpose. That is to say, a wetting agent is employed that is either classed colloidally as having no electrical charge or as being charged colloidally with a positive charge. A neutral wetting agent that has been found to be successful for this type of paper is a distearate of a highly polymerized glycol: other neutral long-chain fatty acid esters may be used. The cationic wetting agents comprise a class consisting of either condensation products of long chain fatty acids and ethanolamines or long carbon chain compounds that contain a tertiary amine group H cg? a quaternary salt of such a tertiary amine. The term long chain fatty acids is applied .to 551059 which are water-insoluble, that is, which have it) or more carbon atoms in the chain: and a corresponding length is used for the other designated long chain compounds. I of such wetting agents in the tanning agent solution facilitates the action of the and produces higher wet strengths in the paper. It has been found experimentally, for example, that a solution containing 2 percent oi. glyoxal and 0.3 percent of a tertiary amine wetting agent. having a trade name of a five-fold improvement in wet rub over a paper sized with the same glue size but treated with 2 percent of formaldehyde.

It has been found that glyoxal and such wetting agents can be employedjointly, without loss of efficiency by ither material.

The presence Ninol," produced purpose of effecting a primary' been found in some instances that spoilage of the coated papers occurs at high relative huinidities when a technical grade of glyoxal is employed; and for such cases it is recommended to employ a the substances in purified condition.

Mixtures of formaldehyd and glyoxal can be used quite satisfactorily for the development of the necessary wet strengths in glue tub-sized papers. A mixture of 1 percent of formaldehyde and 1 percent of glyoxal produces wet tensile strengths intermediate between those obtained with either formaldehyde or glyoxal when used alone,-provided that in the tanning treatment the paper is immersed in the solution of the tanning agents and the excess solution then squeezed on. Iffhowever, the paper is not passed or immersed in the solution but nip of the squeez rolls, one of which rolls is par-- tially immersed in the solution of tanning agent for application to one side only, then the mixture of formaldehyde and glyoxal produces wet strengths higher than those obtained with either of these tanning agents used alone.

' The behavior of glyoxal in reaction with animal and 'vegetable proteins may be seen from the following condensed table of results when animal glue, animal casein, and soybean protein (vegetable casein) have been employed in sizing paper:

Other water-soluble, saturated, aliphatic dials possess tanning action for animal and vegetable protein and are likewise lacking in physiological disadvantages, but they do not appear as eflicient as glyoxal. That is to say, they do not produce as high wet tensile strengthswhen used in equivalent concentrations: for example, a 2 percent solution of succindialdehyde is about the same in efiect as a 2 percent solution of formaldehyde,

7 and a Gpercent solution of methyl glyoxal has tanning agent essentially the same eflect as a 2 percent formaldehyde solution.

It will be understood-that this reaction 01'v a suitable dialdehyde upon such proteins as animal glue and caselns may be employed for purposes other than paper sizing. It is obvious that the illustrative examples are not given as restrictions,

' but. that the invention may be employed in many ways within the scope of the claims.

I claim:

' 1. The process of sizing paper and like material I with an animal glue anplied to a surface thereof,

It is presently preferred to maintain the proand having high wet tensile and wet rub strengths, which comprises passing the glue-sized paper through squeezing rolls with the deposited glue in contact with a rotating squeeze roll which is partially immersed in an aqueous solution containing'substantially yde and glyoxal.

passed directly through the 1 percent each of formaldewater-insoluble long-chain fatty acid with eth- 2. Apaper sheetqhavinga wet tensile strength duct being characterized in in ei'rcess'of substantially 1940 grams per 15 millianolamine, said pro meter width and having a high wet rub value, and that it does not liberate an anion having active being characterized in having thereon a sizing wetting properties in its ionized condition.

comprising the reaction product of animal glue 6. A tanning solution for preparing blueprint .papers having animal gluesize thereon for therewith glyoxal. I

3. The process of producing sized paper of high by attaining uniform high wet tensile and wet sing substantially 0.5 to 2.0

' wet tensile and wet rub strengths for receiving rub strengths, compri the blueprint coatings, which comprises applying percent of polymerized glyoxal, and 0.02 to 0.5 a water-dispersed animal glue solution to the percent of awater-soluble cationic wetting agent. surface thereof; thereafter subjecting the same '1. The process of producing sized paper of high tothe action of an aqueous solution containing wet tensile and web rub strengths for receiving substantially 0.5 to 6 percent of a water-soluble blueprint coatings, which comprises applying a saturated aliphatic dialdehyde selected from the water-dispersed animal glue solution to the surgroup consisting of glyoxal, succindialdehyde and face thereof thereafter subjecting the same to methyl glyoxal, in the presence of a water-soluthe action of an aqueous solution containing ble cationic wetting agent, said wetting agent substantially 0.5 to 6 percent of a water-soluble being characterized in-that it does not liberate saturated aliphatic dialdehyde selected from the an anion having active wetting properties in group consisting of glyoxal, succindialdehyde and the ionized condition, and then subjecting the methyl glyoxal, in the presence of a long-chain treated paper to aging. carbon compound containing a tertiary amine 4. The process of producing sized paper of high and effective as a water-soluble cationic wetwet tensile and wet rub strengths for use as a ting agent, said wetting agent being characterbase for blueprint papers, which comprises apized in that it does not liberate an anion having plying to the material a water-dispersed ani- 5 active wetting properties in the ionized condiecting the treated paper to mal glue solution of pH of about 8 to 9.5 at 9. tion, and then subi temperature of substantially 90 to 115 degrees aging. F., said solution including an alkaline buffering 8. The process of producing sized paper of hi agent, and thereafter subjecting the same to the wet tensile and wet rub strengths for use as a action of an aqueous solution containing subbase for blueprint papers, which comprises apply stantially 0.5 to 2 percent of polymerized glyoxal, ing to thematerial a water-dispersed animal glue in the presence of substantially 0.02 to 0.5 percent solution of pH of about 8 to 9.5 at a temperature of a water-soluble cationic wetting agent. of substantially 90 to 115 degrees F., said soluproducing sized paper of high tion including an alkaline buffering agent, and; thereafter subjecting the same to the action of;

5. The process of wet tensile and wet rub strengths, which coman aqueous solution containing substantially 0.5 zed glyoxal, in the pres-v prises appiying a water-dispersed animal glue v solution having a pH between 3.5 and about 9 to 2 percent of polymeri to the surfaces thereof, and thereafter subiectence of substantially 0.02 to 0.5 percent of a ing the same to the action of an aqueous solution water-soluble cationic wetting agent consisting containing substantially 0.5 to 2 percent of gly- 40 of a condensation product of a water-insoluble oxal in the presence of a water-soluble wetting long-chain fatty acid and an ethanolamine. agent comprising a condensation product of a PAUL B. DAVIDSON. 

